1. Field of the Invention(s)
The present invention(s) generally relates to support structures. More particularly, the invention(s) relates to systems and methods for protection of floorings in shipping containers by utilizing support structures.
2. Introduction
Floors can be used in a wide variety of environments, such as in private homes, in public spaces, and in commercial properties. In particular, shipping containers have floors on which goods or other items are stored. In some cases, the floors of shipping containers can include an upper layer of wood flooring that overlays a plurality of support beams such as cross-members.
A floor provides a foundational base structure that can support weight. In order to protect the floor from damage and protect goods from being damaged by the floor (e.g., moving or storage), different, stronger flooring materials are generally utilized.
Quality, stronger woods, such as Asian hardwoods, are becoming more rare. The reduced availability of such wood has led to a reduction in the quality of the wood flooring supplied to container factories. As a result, container floorings are failing prematurely and flooring repair costs have increased significantly. In some cases, flooring repair costs have become approximately 20% of combined owner and user repair costs. Since the availability of suitable wood (e.g., Asian hardwood) will likely continue to decrease in the future, flooring repair costs will likely increase. In the shipping industry, the poor quality of wood flooring can create significant technical and economic challenges for shipping container owners and users.
FIG. 1 illustrates an example shipping container 100 of the prior art. The example shipping container 100 includes an entrance 102. The entrance 102 can be used, such as by forklift or truck vehicles, to deposit and retrieve goods or other items to be stored in the shipping container 100. As shown in FIG. 1, an X-ray view 104 into the shipping container 100 depicts that the shipping container 100 has a foundational base assembly, such as a floor 106. The floor 106 can be formed by a plurality of support beams, such as cross-members 108, spanning transversally across the width of the shipping container 100. Moreover, as shown in FIG. 1, the floor 106 of the shipping container 100 includes an upper layer of wood flooring 110, such as Asian hardwood flooring.
One solution that has been proposed is to replace all of the flooring of a shipping container with steel. The process, however, is expensive, increases the weight of the shipping container to the point where shipping is prohibitive, and the steel flooring may damage cargo during storage or transit.
Another solution is to move the cross-members 108 closer together. FIG. 2 illustrates an example individual forklift wheel 202 on top of a shipping container floor 204 of the prior art. FIG. 2 can illustrate a wheel contact position in rolling shear. Finite Element Analysis (FEA) modeling can be used to identify a critical load condition that is most likely to result in floor failure. In FIG. 2, the container cross-members 206 and 208 are spaced approximately 11.81 inches or 300 millimeters (mm) apart. The position of the forklift wheel 202 as shown in the example of FIG. 2, applies approximately 83% of the shear load through the local plywood 210 thickness and adjacent to the cross-member 206 (the shear load being applied along plane 212). In this example, the calculated shear stress corresponds to the wheel load×83% divided by the area in shear: Shear Stress=(12,000 lbs.×83%)/(7.48 inches×1.125 inches)=1183.6 pound-force per square inch (psi) average, which compares well to the FEA peak shear value of 1212.83 psi.
Those skilled in the art will appreciate that, when viewing rolling shear, moving the cross-members 108 is not only expensive (requiring adjustments to manufacturing new shipping containers and additional materials), but also is likely to lead to more, not less, damage.
It follows that excessive load or force due to forklift wheels can decrease or shorten the life span of the container wood flooring. The wood flooring may not be practically effective at, or sufficiently capable of, withstanding the load or force.
As discussed above, the poor quality of wood flooring and/or the force from forklift wheels can create significant technical and economic challenges for shipping container owners and users. Conventional approaches taken by container industry suppliers or owners in attempt to address these challenges are discussed below.
One conventional approach involves attempting to replace Asian hardwood with an alternative wood or non-wood product. Various alternatives to Asian hardwood have been suggested, but none have been able to meet the combined strength, production capacity, compatibility with container base structure designs, and/or cost constraints that would make them viable alternatives. There is a lack of promising alternatives under development at this time.
Another conventional approach involves minimizing the use of wood by using steel or mixtures of steel and wood instead. Many designs have been proposed and prototypes have been built using all steel floors or various combinations of steel and wood. Most of them have met functional requirements, but added an unacceptable amount of weight to the container, were incompatible with container assembly line processes, and as a result, were too heavy and/or costly to be used.
A further conventional approach involves reducing the unsupported floor span by adding cross-members. This approach is based on a lack of understanding of the critical failure mode of container flooring, and although intuitively attractive, does not reduce the shear stress levels that cause floor failure. Spans are already short enough that the floor is shear critical (and not bending critical) and further reducing spans does not change this.
Accordingly, there is a need for an improved approach for protecting floorings in containers.